1. Field of the Invention
The present invention relates to a plasma generating apparatus for use in micromachining a semiconductor device and a dry etching method for realizing high precision dry etching processing for fine electrodes, wiring and contact holes on the semiconductor device.
2. Description of the Related Prior Arts
In a semiconductor device manufacturing process, a thin film such as polycrystalline silicon (Poly-Si) or Alxe2x80x94Cu alloy formed on a wafer is micromachined by dry etching to form gate electrodes or metal wiring. For electrical connection between a transistor and a metal wiring, and between metal wirings, formed on the wafer, a contact hole is formed by a dry etching method on an insulating film (a thin film consisting mainly of SiO2 or the like, which will be hereinafter referred to as an oxide film) formed on the transistor construction and between the wirings, so that an electrical conductor is filled in the contact hole.
The above-mentioned dry etching processing is done in such a manner that an etching gas is introduced into a dry etching apparatus as a vacuum chamber, a high frequency bias or microwave (xcexcwave) is applied to the etching gas to generate plasma, and radicals and ions generated in the plasma are used.
In etching, a mask such as a photoresist thin film provided by transferring an electrode pattern, wiring pattern or hole pattern is formed on the oxide film. In dry etching, the Poly-Si film, Alxe2x80x94Cu alloy film or oxide film is selectively processed to the mask or substrate to form a predetermined processing shape.
In recent years, in order to improve the integration density, ability to be treated and productivity of a semiconductor device, making the pattern finer, and increase of the diameter of a wafer to be treated (300 mm in diameter) have been advanced. To cope with increase of the wafer diameter, a plasma generated in a dry etching apparatus must be uniform. To enhance the productivity, the plasma density must be increased to 1011/cm3 or higher. To improve the controllability of the processing shape, a stable plasma must be formed at a gas pressure in a range from 0.2 Pa to 4 Pa. For this reason, the wafer diameter must be large and a plasma which is uniform and has a high density must be generated at a low gas pressure.
In a conventional parallel plate type (capacitive coupled type) dry etching apparatus, however, it is hard to lower the gas pressure. In addition, in a conventional inductive coupled type dry etching apparatus, to obtain a plasma having high uniformity with a large wafer diameter, the distance between the plasma generating source and the wafer must be large, thus it is difficult to increase the density. Further, in a conventional magnetic microwave etching apparatus, the microwave has a short wavelength of about 120 mm, and the microwave node is applied onto the wafer. Thus, it is difficult to realize a uniform plasma with a large wafer diameter.
In the magnetic microwave etching apparatus, a uniform plasma can be obtained by increasing the wavelength of the microwave. The frequency of a high frequency introduced to generate a plasma is changed from a microwave (2.45 GHz) to UHF band (300 MHz to 900 MHz), so that the wavelength of the high frequency introduced is 300 mm or more. There is a possibility of the provision of a uniform plasma which can cope with etching of a large-diameter wafer. In other words, the magnetic UHF etching apparatus may cope with the process for manufacturing a fine semiconductor device of large diameter. The above-mentioned magnetic UHF etching apparatus is disclosed in, for example, U.S. Pat. No. 5,891,252 specification (the cited document 1).
In the above-mentioned magnetic UHF etching apparatus, a disc type antenna is used as means for introducing a UHF wave into a processing chamber. The diameter of the antenna and the thickness of the dielectric are determined such that a UHF wave can efficiently be introduced into the processing chamber, and so as to be resonant with the UHF wave introduced. The uniformity of the plasma generated depends on the diameter of the antenna, the magnetic field conditions (specifically, an electric current flowing to a solenoidal coil) and the gas pressure. Since the range of the magnetic field conditions (coil current) for providing a uniform plasma is small, it is hard to obtain sufficient uniformity when the gas pressure or the UHF power inputted is changed. Further, optimum magnetic field conditions may be different for each apparatus, and the uniformity may be changed by the etching processing time. In particular, this tendency is high under the conditions of the high plasma density (the electronic density is 1011 pieces/cm3 or higher).
In the magnetic UHF etching apparatus, when the equal magnetic field plane in the etching apparatus is of extremely concave type, the ion current density is higher in the center of the wafer than in the peripheral portion of the wafer. In other words, the plasma density is high in the vicinity of the center of the apparatus. When the equal magnetic filed plane is flat to the surface of the antenna, the ion current density is lower in the center portion of the wafer than in the peripheral portion thereof.
A uniform ion current density can be obtained when the coil current is controlled between the magnetic field conditions for providing an ion current density having a concave distribution (which is high in the peripheral portion) and the magnetic field conditions having a convex distribution (which is high in the center portion). Unless the coil current is controlled with an accuracy of about xc2x10.05A, sufficient uniformity is hard to obtain. In other words, the margin of the coil current is small. Thus, it is difficult to obtain sufficient uniformity.
Accordingly, an object of the present invention is to provide a magnetic UHF etching apparatus improved so as to solve the foregoing problems in the conventional magnetic UHF etching apparatus, more specifically, to provide a magnetic UHF etching apparatus in which a plasma generated is uniform and stable, a plasma having a plasma density of 1011/cm3 or higher can be generated, and can etch process a Poly-Si film, Alxe2x80x94Cu alloy film or an oxide film uniformly over the entire surface of a wafer having a diameter of 300 mm or larger.
In order to achieve the foregoing object, the present invention provides a dry etching apparatus comprising means for introducing at least one processing gas into a vacuum processing chamber, exhausting means for exhausting the processing gas to the outside of the vacuum processing chamber, a plate antenna capable of applying a high frequency voltage to the upper portion in the vacuum processing chamber and a plurality of solenoidal coils disposed outside of the vacuum processing chamber, wherein a plasma is generated in the vacuum processing chamber, and the plasma generated is used to etch process a substrate to be treated placed in the vacuum processing chamber, further comprising modulator for coil current for cyclically modulating a coil current flowing to the solenoidal coil.
In the above-mentioned dry etching apparatus according to the present invention, the modulation cycle of the coil current of the modulator for coil current is desirably set to 10 seconds or below.
The above-mentioned dry etching apparatus according to the present invention further includes, instead of the modulator for coil current, coil position control means for repeatedly changing the upward and downward positions (the axial position) of at least one solenoidal coil of the plurality of solenoidal coils.
In the above-mentioned dry etching apparatus according to the present invention, the frequency of the high frequency voltage applied to the plate antenna is desirably set in a range from 300 MHz to 900 MHz.
The present invention provides a dry etching method comprising using a dry etching apparatus including a vacuum processing chamber, vacuum exhausting means for vacuum exhaustion in the vacuum processing chamber, gas introducing means for introducing a gas for etch processing into the vacuum processing chamber, plasma generating generating means for forming the introduced gas in plasma in the vacuum processing chamber, and magnetic field applying means for applying magnetic field into the vacuum processing chamber, and etch processing a substrate to be treated placed in the vacuum processing chamber, wherein the magnitude of the magnetic field applied by the magnetic field applying means is modulated cyclically when the substrate to be treated is etch processed.
In the above-mentioned dry etching method according to the present invention, the cycle of the cyclic modulation of the magnitude of the magnetic field applied by the magnetic field applying means is desirably set to 10 seconds or below.
In the above-mentioned magnetic UHF etching apparatus, the concave distribution to the convex distribution of the ion current density in the plasma generated can be controlled by the coil current flowing to the solenoidal coil. The plasma generated has good stability in the concave or convex distribution, whereby the uniformity of the ion current density is not changed greatly by the gas pressure or the UHF wave introduction power. Thus, when the ion current densities in the concave and convex distributions are added, there is a possibility of the provision of a uniform ion current density distribution. Specifically, a plasma having a concave ion current density distribution and a plasma having a convex ion current density distribution are generated alternately, thereby giving a uniform ion current density distribution.
In the above-mentioned magnetic UHF etching apparatus, the plasma density, more specifically, the ion density radiated onto a wafer (the ion current density) is determined by an outer product (Exc3x97B) obtained by multiplying a magnetic field B applied by means of the solenoidal coil by an electrical field E of the UHF wave. When the frequency of the UHF wave is 450 MHz, the magnetic field B of 160 to 170 gausses and the electrical field E so as to generate an Electron Cyclotron Resonance (ECR) under the magnetic field B are applied to give a high plasma density.
In the magnetic UHF etching apparatus shown in FIG. 1, a magnetic field vector B of the solenoidal coil is in the vertical direction, so that only the horizontal component of the electrical field E of the UHF wave is resonant with the magnetic field B. Due to the construction of an antenna used, the horizontal electrical field component is strong in the peripheral portion of the antenna, as indicated by curve 201 of FIG. 2. When an equal magnetic field plane of 160 to 170 gausses is formed by a coil in parallel with a uniform magnetic field, that is, a wafer top surface and antenna lower surface 301 (straight line 302 of FIG. 3), ECR resonance is strong in the peripheral portion of the wafer. For example, the ion current density distribution on a silicon wafer having a diameter of 300 mm is a concave distribution in which the ion current density is higher in the peripheral portion of the wafer than in the center portion of the wafer, as indicated by curve 401 of FIG. 4.
The electric current of the solenoidal coil is adjusted so that the equal magnetic field plane of 160 to 170 gausses is closer to the wafer surface in the vicinity of the center portion of the wafer (0 mm position) and is moved away from the wafer surface in the peripheral portion (xe2x88x92150 mm position and +150 mm position), as indicated by curve 303 of FIG. 3. In this case, the resonance point in the peripheral portion of the wafer as compared with the center portion of the wafer is moved away from the wafer surface. The ion current density is almost uniform over the entire surface of the wafer, as shown by curve 402 of FIG. 4.
When the equal magnetic field plane of the applied magnetic field in the peripheral portion of the wafer is further moved away from the wafer surface (curve 304 of FIG. 3), the ECR resonance is weaker in the peripheral portion of the wafer. The ion current density distribution is a convex distribution, as indicated by curve 403 of FIG. 4.
The concave distribution of the ion current density can be obtained under the magnetic field conditions in which the equal magnetic field plane is flat, and the convex distribution can be obtained under the magnetic field conditions in which the equal magnetic field plane is concave-shaped. The uniform ion current density can be realized by making fine adjustment of the coil current, by switching (modulating) the coil current values in etching, or by adding the concave and convex distributions of the ion current density. Further, a uniform ion current density distribution as described above can be obtained by changing the height of the solenoidal coil for generating a magnetic field (the upward and downward installation position), instead of using the coil current modulation. Furthermore, the coil current modulation may be employed together with the solenoidal coil position adjustment.
As another method for making an ion current density (plasma density) uniform, when a plurality of (two ore more) coils are used as the magnetic field applying means, at least one coil of the plurality of coils is moved alternately between a position for providing the concave-shaped ion current density distribution and a position for providing the convex-shaped ion current density distribution, and then the concave-shaped ion current density distribution and the convex-shaped ion current density distribution are added.
Other objects and constructions of the present invention and operation and effects obtained therewith will be apparent sequentially in the detailed description by giving the following examples.